Article pubs.acs.org/IECR
Integration of Autohydrolysis and Organosolv Delignification for Efficient Acetone, Butanol, and Ethanol Production and Lignin Recovery Hamid Amiri*,†,‡ and Keikhosro Karimi*,†,§ †
Department of Chemical Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran Department of Biotechnology, Faculty of Advanced Sciences and Technologies, University of Isfahan, Isfahan 81746-73441, Iran § Industrial Biotechnology Group, Institute of Biotechnology and Bioengineering, Isfahan University of Technology, Isfahan 84156-83111, Iran ‡
ABSTRACT: A two-stage pretreatment, i.e., autohydrolysis and organosolv delignification, was used prior to enzymatic hydrolysis and fermentation by Clostridium acetobutylicum for the improvement of acetone, butanol, and ethanol (ABE) production from rice straw, pine, and elm. Through the autohydrolysis, a liquid, “autohydrolysate”, containing 2−7 g/L sugar and 13−27 g/L oligomer, and a pretreated solid were obtained. The solid was subjected to organosolv delignification leading to 490−600 g of pretreated lignocelluloses (70%−74% cellulose) and 100−140 g lignin from each kilogram of lignocelluloses. The pretreated lignocelluloses were hydrolyzed to “cellulosic hydrolysates” and fermented to 6−10 g/L ABE. Through this process, 70−123 g of ABE was produced from each kilogram of lignocelluloses. “Overall hydrolysates” with further sugar concentrations of 16−50 g/L were obtained by hydrolysis of pretreated solid in the autohydrolysate. The yield of ABE production was progressed to 133 g ABE/kg elm by fermenting its overall hydrolysate.
1. INTRODUCTION The overconsumption of the depleting and nonrenewable crude oil resource threatens the accessibility to sources of energy and chemicals in the future, which makes the transition to renewable carbon resources inevitable.1 The only foreseeable resource that can provide a sufficient volume of sustainable carbon without arising the concern of the food versus fuel conflict are lignocellulosic materials.2 However, to produce fuel and chemicals from lignocellulosic resources, efficient technologies should be developed to compete with the fully developed fossil-based technologies.3 Lignocellulosic materials are complex and resistant combinations of cross-linked layers of cellulose, hemicellulose, and lignin.4 Hydrolysis of lignocelluloses to fermentable carbohydrates followed by fermentation of the resulting hydrolysates using different microorganisms to a wide range of metabolites is one of the most promising approaches for production of fuel and chemicals, e.g., ethanol.3 A proper pretreatment followed by enzymatic hydrolysis of pretreated solids is required for obtaining glucose from cellulose fraction of lignocelluloses, which were mostly developed for bioethanol production.5 In addition, the hemicellulose fraction of lignocelluloses can be hydrolyzed to sugars and oligomers through a relatively low cost physiochemical processing. However, this part, 25%−30% of lignocelluloses, is ignored in most processes for ethanol production, in which typical ethanol-producing microorganisms are unable to ferment hemicellulose-derived pentoses.6 © XXXX American Chemical Society
In recent years, acetone−butanol−ethanol (ABE) fermentation by solvent-producing Clostridia has been suggested for the production of biobutanol from lignocelluloses.6,7 As a biofuel, butanol has superior characteristics, in comparison to ethanol. ABE fermentation is one of the first industrially applied bioprocesses that had attracted renewed interest by the time butanol was introduced as an advanced biofuel.8,9 In addition, having the ability to uptake a wide range of sugars and oligomers, the solvent-producing Clostridia can utilize both cellulose and hemicellulose fractions of lignocelluloses for butanol production.6 However, the effect of inhibitors on the solvent-producing Clostridia is more destructive than their effects on the ethanol-producing strains.10 Therefore, the pretreatment and hydrolysis technologies that have been developed mostly for bioethanol production may not sufficiently match with ABE fermentation.6 Delignification of lignocelluloses prior to enzymatic hydrolysis has been suggested for obtaining a hydrolysate fermentable without the necessity of detoxification.11,12 While lignin is the major barrier to the enzymatic hydrolysis of cellulose, this is not its only effect on ABE production from lignocelluloses.11 The more serious problem caused by lignin is in the fermentation Received: January 11, 2016 Revised: March 24, 2016 Accepted: April 7, 2016
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DOI: 10.1021/acs.iecr.6b00110 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
2. MATERIALS AND METHODS 2.1. Raw Materials and Enzymes. The woody materials used in this study, i.e., pine wood and elm wood, were obtained from Isfahan University of Technology Forest (Isfahan, Iran, 32°43′N, 51°32′E). The woody materials were debarked and cut into pieces
